This project concerns the roles of cell cycle checkpoint and DNA repair genes in protecting human cells from mutations and chromosomal aberrations induced by Superfund carcinogens. The "guardian of the genome" and tumor suppressor gene, p53, is now known to coordinate a complex set of checkpoint and DNA repair responses in carcinogen- damaged cells. Sone of the signals to activated p53 function come from the ATM kinase gene product. ATM also signals to p53-independent cell cycle checkpoints. Cells lacking p53 or ATM gene function display genetic instability and increased susceptibility to malignant transformation. Such cells provide a window to the systems of response to DNA damage that protect against human carcinogenesis. One human carcinogen found in many Superfund waste-sites is vinyl chloride (VC). Although not directly reactive with DNA, after absorption and metabolic activation to form chloroethylene oxide (CEO), mutagenic etheno adducts are produced on DNA bases. A subfraction of people exposed to VC in the workplace expressed high frequencies of hprt mutations in blood lymphocytes, while the majority of VC-exposed people did not. We will test whether this elevated mutation frequency is associated with a DNA repair defect by assessing CEO-induced genotoxicity in lymphoblastoid lines derived from sensitive and resistant people. Superfund waste-site carcinogens such as benzene and benzo[a]pyrene can be metabolized within cells to produce reactive electrophiles such as benzene- diolepoxide, respectively, as well as reactive oxygen species (ROS). The electrophiles and ROS both may attack DNA producing mutations and chromosomal aberrations. This project will determine whether p53 and ATM protect against genotoxicity by CEO, ROS, and diolepoxides. Enhanced risk of development of breast cancer has been linked to mutations in genes that participate in DNA repair including p53 and ATM. This project will employ a functional assay for DNA repair capacity in peripheral and lymphocytes that measures rejoining of radiation-induced chromatid breaks. This assay will be used in a case- control study to test the hypothesis that development of breast cancer is associated with a defect in DNA repair. Sensitive cells identified in our case control study will be available as immortalized lines to determine whether hypersensitivity extends to ROS induced by Superfund carcinogens.